For generations, homes were framed with timber, with the interiors clad in drywall or some sort of wallboard. In a traditional wood-framed home, hanging things from the walls was neither difficult nor precarious. Mainly 2″×4″s and 2″×6″s were used. After the framing was finished, drywall or some wall board surface would be attached to the framing members, it would be painted and then the millwork would be attached, such as a kitchen cabinet, a bathroom vanity, book cases etc. These solid wooden studs were sturdy and the process, although wasteful, allowed builders and homeowners alike to easily fasten millwork and other heavy objects to walls by using a wood screw to connect the millwork to the structural timber framing members of the home. The solid wood stud provided plenty of surface contact to a fastener or wood screw and plenty of tensile strength to hold the fastener or wood screw in place and support the weight of e.g. cabinets and shelves being fastened to the walls. The use of a solid wood stud and a properly sized wood screw remains the preferred and usual method to install carpentry and millwork.
Wood screws typically have a straight shaft or body with a consistent diameter having a pointed tip at on one end and with a regular spaced thread winding its way up the shaft to the head of the screw located at the end opposite the pointed tip. Wood is somewhat elastic and tends to hold its form. The straight shaft and regular thread of the wood screw in turn allows the screw to squeeze between the wood fibers of a solid wood stud, giving plenty of surface contact between the wooden framing member and the screw and allowing the wood stud to hold it along its whole surface. This is why wood screws in wood framed homes work well.
Many other kinds of threaded fasteners exist with these fasteners being distinguished by their varied tightening features, shaft profiles, thread pitch, thread profile, terminal piercing and cutting features and the materials the fasteners are made of. For example, sheet metal screws designed for use with sheet metal are also known. These screws are similar to wood screws in that they typically have a straight shaft, consistent diameter leading to a pointed tip and a regularly spaced thread.
When a lighter object is to be hung, a drywall anchor can used instead. With its small pilot hole, a drywall anchor can be twisted straight into wall board regardless of the location of stud. In fact, it is preferable when using wall anchors to avoid the wood studs entirely as they are designed to be applied strictly to drywall. However, drywall anchors are generally load rated at only around 50 lbs.
In recent years, builders have begun using steel framed partitions in structures like condominiums and commercial towers. Steel stud construction is popular with builders of condos, offices and even some homes because it saves lots of time and materials for builders and homeowners alike, resulting in cost savings and more efficient use of labor. Most high-rise structures in cities today are framed this way.
Steel stud construction is not without its problems, however. For example, the light gauge and weight of the steel studs has made it extremely difficult and time consuming to fasten most things to walls. (e.g. cabinets, shelves, artwork, large screen televisions, pictures). A typical interior partition framed with steel studs has a drywall face just like the wooden framed wall but the studs inside are hollow and quite flimsy. Viewed in section from above, a steel stud looks like the letter “C”, as steel studs are closed on 3 sides and hollow. Steel studs only become structurally strong when fastened to the cement slab above and below (or the floor and ceiling) as well as attached to the other framing members, drywall or wallboard. In other words, steel framed structures become strong when assembled in unison with the other building components.
Conventional wood or sheet metal screws were not designed for use with a thin, hollow steel stud because the steel stud offers little surface contact/contact substance for the screw threads to hold on to. When coupled with the fact that the steel studs are quite malleable and easily distorted, the result is a poor match of fastener and framing member. The wood and sheet metal screws stretch the hole they make in a steel stud and then can't be properly snugged up. Further, the wood and sheet metal screws strip easily and they do not secure well to the sheet metal that is within a wall. As a conventional metal or wood screw is tightened in a steel stud, it winds in adequately, but when an attempt is made to turn the thread a final time to secure the screw in the steel stud, the metal of the steel stud is displaced and the slender straight screw easily slips loose.
Drywall anchors designed for use in drywall, are no better in steel studs. Drywall anchors are designed to cut into the gypsum wall board and hold tight like a plug. These screws are often too short to reach the steel stud behind the drywall. When they can be threaded into a hole in a steel stud, they have similar issues as wood and sheet metal screws, such as tearing of the hole and stripping of the screw. Further, drywall anchors are only rated for light weight applications.
To address the problem of fastening millwork to steel studs, builders have come up with a number of work-arounds, but these work-arounds have proven time consuming and costly, with none addressing the problem directly or effectively. A commercial builder often winds up applying a layer of plywood behind the drywall on the face of the steel studs to give the millwork installers something to screw the cabinets to. In other cases, the studs are cut and altered and a strip of plywood is placed along the face of the studs behind the drywall. These alternatives are slow, time consuming, indirect and also quite pricey, not to mention inferior to simply screwing into wooden studs. A contractor installing anything heavy in a steel framed home or office likely will need to open the wall and pack some wood of their own inside the framing behind the drywall to give something to screw into that will hold fast. This means that before e.g. the millwork can be installed, the wall must first be cut open, the wood put inside and then the drywall must be painted and plaster repaired. Builders have also used combinations of construction adhesives and toggle bolts or butterfly clips applied through the drywall to hang e.g. millwork, but these still are only rated for only about 250-275 lbs depending on the gauge of the hardware.
Thus, there is a need for a fastener that can fasten securely in a steel stud and can secure heavy objects, such as large TV's, cabinets and bookshelves.
As discussed in the present application, “millwork” refers to a wooden wall furnishings, including bookshelves and cabinets. “Wall cladding” refers to a plurality of generally planar materials fastened vertically to vertical support studs, exemplified by gypsum wallboard. “Steel studs” are vertical struts formed by the folding of sheet metal to resist bending. When fastened from floor to upper beam, said steel studs form walls to which wall cladding, generally gypsum wallboard, and millwork, such as cabinets, are applied. An “anchor” refers to a fastener that forms a mate with a substrate, such as drywall to bear a load. The “mate” refers to the piercing and threading into a substrate of a threaded fastener, also called a “screw”, exemplified by a screw mated to a wall by driving it in with a screwdriver, whether manual or power-driven. “Linear” describes the relationship of a dependent variable increasing in a straight line function with an increase in the independent variable. “Non-linear” refers to the relationship function described by a curve.
The “tightening features” refers to the openings in the head of a fastener into which a drive bit is fitted to enable rotation of the screw head, with the screw head being a flanged accoutrement crowning a threaded shaft. The “shaft profile” describes the change of diameter of the shaft down the length of the shaft. Known shaft profiles include a shaft with a meeting of two straight lines, a “linear” shaft, or two curves (i.e. “non-linear” shaft). Generally conical shafts equipped with helical threads will translate a rotational force applied to the head into a perpendicular linear displacement into the material to which the fastener is applied. The “thread pitch” describes the number of rotations of the thread per linear unit of shaft length. An “aggressive” thread has a widely spaced helical ridge. Thread can be “linear”, that is, unchanging along the length of the shaft, or “non-linear”, wherein the thread count varies along the long axis of the fastener shaft. “Thread profile”, the cross-sectional shape and dimensions of the thread ridge as it winds around the shaft, can be uniform or non-uniform along the thread helix. Changing thread pitch and thread profile along the shaft can result in different qualities of mate between the fastener and the material being fastened into. The choice of “materials” can affect the hardness, brittleness, and tensile strength of the fastener, all of which will determine the quality of the mate with the substrate into which the fastener is fastened. Finally, at the terminal point of the shaft a plurality of “cutting” features and “piercing” features can be incorporated to add the entry of the fastener into the substrate. Said cutting and piercing features are affected by materials and geometry.
Lopez (U.S. Pat. No. 4,473,984: Oct. 2, 1984) presents a threaded stud that is meant to penetrate any masonry, wood, or steel stud wall to present a loop transverse to the stud thread helix emanating from the wall said threaded stud has penetrated. While no claims or description are made of the threaded stud, the patent specification does identify that the manner of thread and cutters can influence the thread mate. Diagrams for this patent indicate a threaded stud or shaft that is identical in cross-section from base to just before the conical pointed tip. Non-linear shaft profiles, linear thread pitch progressions, non-uniform progression of thread profile are all not discussed in terms of their influence on mate between the anchor and the wall. The threaded stud of the Lopez patent would not be suitable for fastening with a steel stud for the same reasons as a wood screw or sheet metal screw. The thin steel stud would distort easily with the described threaded stud with the point of entry (pilot hole) being easily displaced, such that this fastener would lose its grip and not secure properly
Bui (U.S. Pat. No. 8,601,763: Dec. 10, 2013) describes a novelty specific to the metal studs discussed in this Application. The rivets or screws of the Bui patent purportedly connect a thin concrete slab to a metal frame. Thus, the Bui patent describes a rivet to be applied between ribs of a steel stud into screws supported a concrete panel can be drilled. This static implementation of a mate in the steel stud itself presupposes the ability to find this mate rivet when hanging the wall cladding to the steel studs. Such a fastener is very specifically designed for mating concrete to metal and would not be appropriate for e.g. drywall as it would break apart the drywall and therefore would not tighten properly in a steel stud application.
Katsumi (U.S. Pat. Application 20060228186: Oct. 12, 2006) presents a self-tapping stainless steel screw with a built-in fracture line to remove the drill head when drilling steel sheets for rooves and walls. What the steel sheets are being affixed to is not specified. No special attention is given to the thread, the thread profile, and the shaft profile, and the material used is not zinc. Such a fastener would not be suitable for fastening with a steel stud for the same reasons as a wood screw or sheet metal screw. The screw of the Katsumi patent is designed for use with heavier gauge studs, for example the kind used in roofing truss, which is much heavier/thicker than the steel studs used behind an apartment's walls. The straight shaft and even threads of this screw would strip easily in a steel stud. Further, these screws would work well in shear forces but would not tension, because the cross section of the amount of material the threads grab is minimal.